You asked
Sigma 50mm f 1 4 dg hsm art vs sony fe 50mm f 1 4 gm?
On paper these two are very close. Both are 50mm f/1.4 autofocus lenses for full frame, and neither has stabilisation. Both also give the same view on Sony APS-C, roughly 75mm with depth of field like f/2.1.
The difference is mounts. The Sigma 50mm f/1.4 DG HSM Art comes in Canon EF, Nikon F, Sony E and L-Mount, so it's the one to consider if you might switch systems or already shoot Canon or Nikon. The Sony FE 50mm f/1.4 GM is Sony E only. If you shoot a Sony body, it's the native choice, and the mount alone won't separate them.
I can't give you a verdict on image quality from this site's pages, so check reviews before you buy. If you're mainly shooting people, both fit the portraits advice for a fast 50mm.
Written by Claude from this site's pages.